Deaf individuals represent a unique linguistic population in that there is wide variation in when they are first exposed to language. Although it is well established that deaf children without access to language from an early age are at-risk for delays in language, literacy, and other academic outcomes, as yet there is very little known about how sign language is processed in deaf individuals, and how processing ability may affect vocabulary and other linguistic skills. This is particularly important in light of the fact that over 90% of deaf children are born to hearing parents, and thus their early linguistic environment is highly atypical and frequently impoverished. The proposed study will investigate sign language processing through development of a novel paradigm. The paradigm is an adaptation of the "looking-while-listening" (LWL) paradigm that has been used with hearing subjects from infants to adults. The LWL paradigm yields time- course measures of children's responses at higher temporal resolution than is common in other widely used experimental tasks. Children look at pairs of pictures while listening to speech naming one of the pictures, and gaze patterns are videotaped and analyzed in relation to the concurrent speech signal. In addition to measures of accuracy, the LWL procedure yields precise measures of the speed, or reaction time (RT) with which subjects initiate a shift in gaze to the target picture relative to the onset of the target word. Despite the established validity of this paradigm and significant gains in understanding it has provided, to date there has been no attempt to assess parallel developments in sign language processing. In the proposed study, this paradigm will be adapted for use with American Sign Language (ASL). Thus instead of an audio speech signal, subjects will see a signed signal labeling one of the pictures. Gaze shifts will then be used to obtain measures of processing efficiency in deaf individuals using ASL. The goal of this project is to obtain data on real-time processing of sign language by deaf children and adults, a measure that cannot be obtained using current experimental paradigms. Specifically, the objectives of the study are: 1) to investigate real-time processing of ASL by deaf adults and children who have been exposed to language from birth (i.e. from deaf parents), comprising typical development;2) to reveal possible differences in processing in adults and children who acquire ASL at later ages (i.e., from hearing parents);and 3) to determine the relationship between processing efficiency and ASL skill. This novel paradigm will begin to fill a critical gap in knowledge about how ASL is processed by both typical and atypical language learners. Understanding how sign language is processed in these populations will reveal important insights about critical period phenomena, processing of visual language, and relationships between language processing ability and vocabulary development. PUBLIC HEALTH RELEVANCE: The proposed project will examine how deaf adults and children process American Sign Language (ASL), and whether there are differences in language processing between individuals who have deaf parents and are exposed to ASL from birth, and those who have hearing parents and are exposed to ASL after birth. This study will have implications for early identification and education practices for deaf children, and will contribute to our understanding of language comprehension in different populations, critical period effects on sign language processing, and the potential negative effects of early language deprivation. )